1. Field of the Invention
The present invention relates to subsea pipelines and connectors and/or fittings used in the pipelines. Some embodiments relate to fittings to combine and/or redirect flow in the pipelines. More particularly, the invention relates to a subsea fitting used to facilitate pigging and/or cleaning of subsea pipelines.
2. Description of Related Art
Offshore pipeline systems are a maze of connected and interconnected pipeline segments that transport hydrocarbons or related products from one point to another. The pipeline connection points initiate at the wellhead and connect to subsea manifolds, offshore structures, and, eventually, to land for final processing and distribution of the products. Due to the expenses of running dedicated pipelines from the initiating point direct to processing stations, shorter pipeline segments are joined to existing or larger pipelines to create the product pipeline from the source (e.g., the initiating wellhead) to the market (e.g., onshore stations).
Pipeline interconnects have been accommodated by placing tee-shaped fittings with a perpendicular intersect into a pipeline to create what has been known as a branch or lateral connection point. These connections provide a means of combining the product from one line with another. However, these connections do not allow for the passage of certain pigs used for cleaning and inspection, sometimes referred to as solid-mandrel, trained, or intelligent pigs. Combining the flow of two pipelines into one line to allow for pigging by all common forms of pigs requires the use of a fitting known as a piggable wye.
Piggable wye fittings have relatively shallow intersect angles, typically about 30° or less, which allow for fairly smooth transmission of long pigs and pig trains from either of the two inlet bores through the intersect and out through a common exhaust. However, if a pig is ever run into the piggable wye in a reverse direction, the pig will jam in the intersect of the wye, abnormally shutting down the pipeline.
Reverse flow of a pipeline is becoming increasingly more common. To this end, the ability to pig in the reverse flow direction is becoming a more common consideration for pipeline design. Thus, a piggable wye fitting that can be configured to suitably pass all forms of pigs in normal (e.g., combining) flow conditions and in reverse (e.g., directed) flow conditions is desirable.